Inflammatory cytokines are produced by innate immune cells and play a key role in host defense, inflammation and the transition from innate to acquired immunity. Expression of multiple inflammatory cytokines and chemokines by innate immune cells is induced by microbial products and endogenous inflammatory factors that utilize conserved NF-?B and mitogen-activated protein kinase (MAPK) signaling pathways. The long term goals of this project are to elucidate mechanisms that control inflammatory cytokine production in macrophages and dendritic cells, with an associated goal of developing new therapeutic approaches to modulating cytokine production during immune responses and inflammation. The importance of selective regulation of macrophage and DC responses to ensure they are most appropriate for the environment and elicit the effective host responses to specific microbial pathogens has been increasingly appreciated. Mechanisms that focus cytokine production to generate the most appropriate responses are just beginning to be understood, but appear to involve cooperation/crosstalk between different receptors that sense microbial stimuli, and the utilization of transcription factors, such as interferon regulatory factors (IRFs), that modulate the activation and outcomes of NF-?B and MAPK signaling. In the course of our investigation of signal transduction crosstalk in the regulation of macrophage cytokine production, we found that the Notch signaling pathway cooperates with TLR-induced pathways in the activation of a subset of TLR-inducible genes. Notch and TLR signaling was integrated at the level of the DNA binding protein RBP-J. RBP-J was previously known as a key mediator of the canonical Notch signaling pathway important in the induction of classical Notch target genes. We found that deletion of RBP- J resulted in attenuated expression of approximately 12% of TLR-inducible genes, including TNF, IL-6 and IL-12. Strikingly, the genes most highly dependent on RBP-J for TLR-induced expression included genes important for host defense against intracellular pathogens and Th1 responses: Il12a (encoding IL-12 p35), Il12b (p40) and Nos2 (iNOS). Expression of these genes is regulated by IRF1, IRF8 and the NF-?B family member c-Rel. Thus, RBP-J is required for the acute induction of a subset of TLR-inducible genes that share common functions and regulatory mechanisms. In addition, RBP-J suppressed activation of calcium- dependent calcineurin (Cn)-NFAT signaling that is associated with alternative differentiation into myeloid cells that are refractory to TLR-induced activation of inflammatory cytokine production. In this application, we will investigate mechanisms by which RBP-J regulates cytokine production, and the functional importance of this regulation. We anticipate that these studies will yield insights about specific regulation of subsets of TLR-inducible cytokines and genes that will be useful in developing therapeutic approaches to modulate specific innate immune functions.